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Mosquitoes rely mainly on the olfactory system to track hosts. Sensilla contain olfactory neuron receptors that perceive different kinds of odorants and transfer crucial information regarding the surrounding environment. Anopheles maculatus and An. sawadwongporni, members of the Maculatus Group, are regarded as vectors of malaria in Thailand. The fine structure of their sensilla has yet to be identified. Herein, scanning electron microscopy is used to examine the sensilla located on the antennae of adults An. maculatus and An. sawadwongporni, collected from the Thai-Myanmar border. Four major types of antennal sensilla are discovered in both species: chaetica, coeloconica, basiconica (grooved pegs) and trichodea. The antennae of female An. maculatus have longer lengths (μm, mean ± SE) in the long sharp-tipped trichodea (40.62 ± 0.35 > 38.20 ± 0.36), blunt-tipped trichodea (20.39 ± 0.62 > 18.62 ± 0.35), and basiconica (7.84 ± 0.15 > 7.41 ± 0.12) than those of An. sawadwongporni. Using light microscopy, it is found that the mean numbers of large sensilla coeloconica (lco) on both flagella in An. maculatus (left: 32.97 ± 0.48; right: 33.27 ± 0.65) are also greater when compared to An. sawadwongporni (left: 30.40 ± 0.62; right: 29.97 ± 0.49). The mean counts of lco located on flagellomeres 1-3, 6, and 9 in An. maculatus are significantly higher than those of An. sawadwongporni. The data in this study indicate that two closely related Anopheles species exhibit similar morphology of sensilla types, but show variations in length, and likewise in the number of large sensilla coeloconica between them, suggesting they might be causative factors that affect their behaviors driven by the sense of smell., Competing Interests: Declaration of competing interest All authors of this manuscript declare that we have seen and approved the submitted version of this manuscript. The authors report no conflicts of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The occurrence and spread of insecticide resistance has had a negative effect on the efficacy of insecticide-based tools and is distributed worldwide, including the Greater Mekong Subregion (GMS). This study aims to determine the insecticide susceptibility of malaria and dengue vectors in malaria and dengue hotspots on the Thai-Myanmar border. Mosquito larvae and pupae were obtained from water sources from December 2019 to April 2020 in Tha Song Yang District, Tak province, western Thailand. WHO bioassay susceptibility tests were conducted with three classes of insecticides to evaluate the knockdown and mortality rates of Anopheles and Aedes aegypti female adults. V1016G and F1534C kdr mutations in the voltage-gated sodium channel of Ae. aegypti were identified using a multiplex PCR. A total of 5764 female mosquitoes were bioassayed in this study, including Anopheles spp. (92.63%) and F1 Ae. aegypti (7.37%). After 24 h of observation, An. minimus s.l. ( n = 3885) and An. maculatus s.l. ( n = 1138) in Suan Oi (SO) and Tala Oka (TO) were susceptible to pyrethroids, organophosphates and carbamates (except bendiocarb) with 98-100% mortality (MR). Resistance to bendiocarb was detected with a mortality rate of 88.80%, 88.77%, and 89.92% for An. minimus s.l. ( n = 125, 125) and An. maculatus s.l. ( n = 66), respectively. The first generation of Ae . aegypti adult females were suspected of resistance to deltamethrin ( n = 225, MR = 96.89%) and confirmed resistance to permethrin ( n = 200, MR = 20.00%). V1016G and F1534C mutations were detected in three genotypes, heterozygote and homozygote forms. The correlation between the kdr alleles and deltamethrin resistance was significant. In conclusion, bendiocarb resistance was found in primary malaria vectors, An. minimus s.l. and An. maculatus s.l. F1 Ae. aegypti population was pyrethroids-resistant, associated with kdr alleles. Therefore, molecular analysis should be conducted to gain insights into the mechanism of insecticide resistance. Routine malaria vector control programmes, such as fogging implementation in hotspot villages to induce Aedes resistance available in peri-domestic sites, are questionable.

Anopheles kochi Dӧnitz (Diptera: Culicidae) is a malaria vector in some countries in South and Southeast Asia. This is the first report to provide clear evidence that two different cytological forms of An. kochi are conspecific based on systematic studies. Two karyotypic forms, i.e., Form A (X 1 , X 2 , Y 1 ) and a novel Form B (X 1 , X 2 , Y 2 ) were obtained from a total of 15 iso-female lines collected from five provinces in Thailand. Form A was common in all provinces, whereas Form B was restricted to Ubon Ratchathani province. This study determined whether the two karyotypic variants of An. kochi exist as a single or cryptic species by performing cross-mating experiments in association with the sequencing of the second internal transcribed spacer (ITS2) of ribosomal DNA (rDNA), and cytochrome c oxidase subunit I (COI) of mitochondrial DNA (mtDNA). Cross-mating experiments between the two karyotypic forms revealed genetic compatibility by providing viable progenies through F 2 generations. The two forms showed a high sequence similarity of those two DNA regions (average genetic distances: ITS2 = 0.002-0.005, COI = 0.000-0.009). The phylogenetic trees based on ITS2 and COI sequences also supported that four strains (from Bhutan, Cambodia, Indonesia, and Thailand) were all of the same species. Five sensilla types housed on the antennae of female An. kochi were observed under scanning electron microscopy (SEM). In addition, this study found that An. kochi was a refractory vector, revealed by 0% susceptibility rates to infection with nocturnally subperiodic Brugia malayi. The cibarial armature was a resistant mechanism, as it killed the microfilariae in the foregut before they penetrated into the developmental site., Competing Interests: Declaration of Competing Interest All authors declare that we have no conflict of interest., (Copyright © 2019 Elsevier B.V. All rights reserved.)